Cancers are the commonest cause for death among all of the causes for death, and the main therapies therefor are palliative treatment in which surgical treatment is combined with radiotherapy and chemotherapy. By virtue of the advance in medical technology, cancers have become such diseases that can be highly possibly cured if they can be found in the early stage. Therefore, a detection method of cancer which can be easily carried out by testing serum, urine or the like without physical and economical burden to patients is demanded.
Recently, methods wherein tumor products such as tumor markers are measured have been widely used as diagnostic methods using blood or urine. Examples of the tumor product include tumor-related antigens, enzymes, specific proteins, metabolites, tumor genes, products of tumor genes, and tumor-suppressor genes. In some cancers, a carcinoembryonic antigen CEA, glycoproteins CA19-9 and CA125, a prostate-specific antigen PSA, calcitonin which is a peptide hormone produced in thyroid and the like are utilized as tumor markers in cancer diagnosis. However, in most types of cancers, there are no tumor markers useful for cancer diagnosis. Further, since most of the tumor markers currently known exist only in very small amounts (e.g., in the order of pg/mL) in body fluid, their detection requires a highly sensitive measurement method or a special technique. Under such circumstances, if a novel cancer test method by which various cancers can be detected by simple operations is provided, its use for diagnosis of various cancers are expected to be developed.
The method would be very useful if it further enables diagnosis of cancers developed in invisible parts, assessment of the stage of cancer progression, assessment of the grade of cancer malignancy, follow-up of postoperative patients, diagnosis of recurrence, diagnosis of metastasis, monitoring of therapy and the like, in addition to detection of cancers.
More particularly, if a method which enables diagnosis of cancers developed in invisible parts is provided, it would be useful for early detection of cancers in parts where cancers are hardly realized, for example, the inside of the abdominal cavity. Further, even in cases where the tumor is too small to be found visually, detection of such cancers that cannot be found by ultrasonography, CT (computed tomography) or MRI (magnetic resonance imaging) is also made possible.
The stage of cancer progression is classified based on the extent of expansion of the tumor at the primary site and whether or not metastasis has occurred to a regional lymph node or a distant organ. In general, the disease stage is classified into 5 stages, wherein a larger number indicates a more advanced state. Although, strictly speaking, the definition varies depending on organs, the disease stage 0 indicates a cancer staying within epithelium and the stage 1V indicates a cancer with distant metastasis. If the stage of cancer progression as described above can be determined, determination of an appropriate therapeutic strategy and, in addition, assessment of therapeutic effects of anticancer drugs are made possible. In regard to the determination of the therapeutic strategy, for example, some of prostate cancers are low malignant and hardly progress, hence do not require treatment; and others are progressive and metastasize to bones and/or the like, causing pain and death of patients. Since hormonotherapy and extirpative surgery are accompanied by side effects, it is necessary to appropriately judge and determine the therapeutic approach. Further, if whether the selected anticancer drug is appropriate or not, when to end the administration of the anticancer drug and the like can be appropriately judged, the physical and economical burden on the patient can also be reduced. Therefore, it is important that the stage of progression can be assessed.
One of the characteristics of cancer cells is blastogenesis, that is, dedifferentiation. Except for a part of cancers, lower-differentiated cancer cells such as those poorly differentiated or undifferentiated grow more rapidly after the metastasis, and the prognosis is poor. Such cancers are said to be highly malignant. Conversely, highly-differentiated cancer cells, that is, those showing a high degree of cell differentiation maintain the structural and functional traits of the organ from which they were originated, and can be said to be less malignant. If such cancer malignancy can be determined, it is made possible to secure a larger margin of excision of the tumor in cases where its malignancy is high even if the size of the tumor is small, as well as to follow up the patient, paying attention to larger areas in the surrounding tissues.
In cases where diagnosis of the postoperative course including recurrence and metastasis is possible, diagnosis of whether the tumor has been completely excised by the operation is made possible. Since recurrence is likely to occur in cases where the excision was incomplete, this can be used as a basis for judging whether a more careful follow up of the patient at short intervals is necessary and, in some cases, for deciding whether an early reoperation should be carried out. Furthermore, recurrent cancer can be found at its early stage with a high possibility. In the case of distant metastasis, its detection is likely to be late, but if a method which enables diagnosis of metastasis is provided, a basis for deciding whether the region to be checked should be extended in addition to the site where the tumor was excised and the vicinity thereof can be obtained.
If monitoring of therapy is possible, an appropriate therapeutic method or combination of therapeutic methods can be selected among various therapeutic methods to optimize the therapy. If one can see the therapeutic effects of anticancer agents, selection of the dosing periods and the types and doses of anticancer agents may be made easier. Further, after excision of the tumor, one can know presence/absence of remaining tumor, and during follow up of the patient, one can have a clue to find metastasis or recurrence as early as possible, so that initiation of early treatment is possible. If monitoring of a therapeutic effect is possible, whether the therapeutic approach was appropriate and whether the therapeutic approach should be changed to another can be judged.
It is known that dogs age 7 times faster than human. Recently, a companion animal is kept as a member of a family and often has a lifestyle similar to that of its owner. Therefore, if the companion animal is suffering from cancer, it is possible to predict that the owner has a high risk of development of cancer in the future. If accurate diagnosis of cancer in companion animals is possible, it is expected to be useful as a clue for prophylaxis of cancer in the owners.
It is said that about 6,390,000 and about 17,640,000 dogs are currently kept in Japan and the U.S., respectively. Since, in addition to rabies vaccination, combination vaccines such as pentavalent, heptavalent and octavalent vaccines have become popular, occurrence of highly lethal infectious diseases such as canine parvovirus infection, canine distemper virus infection, canine parainfluenza (kennel cough), canine adenovirus type II infection (kennel cough), canine infectious hepatitis, canine coronavirus infection and leptospirosis decreased. Therefore, the average life expectancy of dogs increased, and aged dogs of 7 years old or older occupy 35.5% of the total number of the kept dogs. As the causes of death, cancer, hypertension, cardiac diseases and the like are consistently increasing like in human. In the U.S., about 4,000,000 dogs/year are diagnosed as cancer, and it is also said that about 1,600,000 dogs in Japan potentially have a certain tumor.
However, there exist no simple diagnostic agents for animal cancers so far, and in the field of animal healthcare, test methods such as photography by X-ray, CT and MRI are not commonly used. Their diagnosis is carried out by palpation, simple blood test and a test by radiography, which largely depend on experience of a veterinarian. Although some veterinarians have begun to employ a test method using serum, human tumor markers are used in the method since canine tumor markers have not been found yet.
Accurate diagnosis of cancer requires an abdominal operation, and there are large problems of the physical burden to a dog and the economical burden to its owner. If diagnosis of cancers can be conveniently carried out in companion animals such as dogs and cats, early detection and accurate diagnosis of the cancers are made possible, which is useful for treatment of the cancers in the companion animals. Further, if a method which enables such simple diagnosis of cancers using serum is provided, it is expected that the method not only makes it possible to diagnose cancers but also contributes a great deal to periodic health examination, preoperative diagnosis and determination of the therapeutic strategy.
Unlike in human, medical examination is not popular in companion animals. Therefore, in many cases, tumor in a companion animal is found at its late stage, and the owner realizes the tumor and takes his animal only after the tumor has grown bigger. In cases where the grown tumor is malignant, surgical therapy such as operation and administration of an anticancer agent or the like are very often too late. Therefore, in cases where the cancer was judged as malignant by a veterinarian, anticancer drug therapy is generally carried out without operation. Even in cases where an operation is carried out, the operation must be strictly controlled to secure the margin and prevent dispersion of blood and cells during the operation. It is desirable to start anticancer drug therapy immediately after the operation and to follow up the patient at short intervals. It is expected that early detection of cancers is made easier if the above-described diagnosis is adopted into the medical examination of dogs, so-called “dog dock”, which is recently being popularized.
On the other hand, in the case of a benign tumor, an operation can be decided to be carried out even if the tumor is large. All that is required is to care the excised area, and there is no need for treatment with neither expensive anticancer drugs nor being nervous about the follow up.
In view of the above-described circumstances, if a simple means for detecting cancers with a high sensitivity which can be applied to cancer diagnosis in animals is provided, accurate and efficient therapy is made possible, which is highly advantageous to both owners and veterinarians.    Non-patent Literature 1: Investigation by Ministry of Health, Labour and Welfare, 2004    Non-patent Literature 2: Nikkei Science, 2007, March, pp. 80-88    Non-patent Literature 3: Clinical Tests, 2003, December, vol. 47, No. 13, p. 1641-1654    Non-patent Literature 4: Statistics of Diseases of Dogs and Cats, 2005, January    Non-patent Literature 5: Companion Animal Health Products: 2006 Edition By Tim Wesley, ANIMAL PHARM REPORTS    Non-patent Literature 6: Expansion of Cancer and Stage of Progression. Hideaki Tsukuma, Department of Cancer Control and Statistics, Osaka Medical Center for Cancer and Cardiovascular Diseases    Non-patent Literature 7: Proteins, Nucleic Acids and Enzymes, vol. 50, No. 11, p. 1405-1412    Non-patent Literature 8: J Cell Sci. 115: 1825-35    Non-patent Literature 9: Blood. 95: 1788-96    Non-patent Literature 10: Mol Endocrinol. 9: 243-54 (1995)    Non-patent Literature 11: J Cell Biol. 145: 83-98 (1999)